It is proposed to study the behavioral effects of various abused hallucinogens (derivatives of tryptamine and phenylisopropylamine) and related compounds by investigating their discriminative stimulus properties and their ability to generalize to LSD stimulus. Agents which are found to produce interceptive cues similar to those produced by LSD, indicating a possible common mechanism of action, will be the subject of further investigation. Serotonin receptor affinities (employing the isolated rat stomach fundus preparation), will be determined and compared. Novel compounds which possess, within the same molecule, features related to more than one class of hallucinogens, are proposed for synthesis. The behavioral effects of these compounds will be examined and should aid in determining whether various hallucinogens act via a common mechanism. Compounds which do not generalize to the LSD (or 5-OMe DMT) stimulus will be examined as potential antagonists.